Inside a jet engine

Harry Dayantis


What's behind the engines that keep planes in the air?

In a new animation launched today, Oxford University engineers take viewers on a tour around the modern jet engine, exploring the qualities that enable fast and efficient air travel.

The animation, 'Jet Plight', is the latest in a series of videos from Oxford Sparks, a web portal giving people access to some of the exciting science happening at Oxford University.

It follows the adventures of Ossie, a friendly green popsicle who has previously been on a spin around the brain, met a rogue planet and negotiated a volcano's plumbing system, as well as investigating heart attacks, the coldest things in the universe, and the Large Hadron Collider.

I caught up the project's scientific adviser, Professor Peter Ireland of Oxford University's Department of Engineering, to find out more about the science behind the animation.

OxSciBlog: What makes jet engines such a fascinating area of research?
Peter Ireland: Many things - for example, the way in which engines are designed to deal with extremes of pressure, temperature and rotational speeds. The gas flow inside the turbine needs to be precisely controlled and this means we need to understand the way it behaves.  We use sophisticated computer models to predict these flows and experiments to understand the flow physics.
OSB: What made you decide to get involved with Oxford Sparks?

PI: I want people to see that engineering is an exciting, important subject and to encourage more schoolchildren to consider it as a career. There’s a real shortage of women going into engineering, so if this animation causes even one girl to consider a career in engineering then I’d consider it a success. There are fantastic opportunities for young people in this country, with a great demand for engineering graduates. Aerospace manufacturers are always looking to recruit new engineers to fulfil their ever-growing order books.

OSB: Why is it so important to make blades from a single crystal of metal?
PI: If you steadily try to stretch most metals, over time they extend slowly - or creep. Creep gets much easier at high temperatures, and the way a blacksmith works high temperature steel is a good example of how metal deformation gets easier with heating. Most metals are made of tiny individual crystals, and creep often occurs at the boundaries between crystals. Creep is reduced if the metal part is made of a single crystal.
OSB: What makes Oxford's turbine test facilities so special?

PI: Our research has focussed on understanding the way in which engine parts perform - especially the turbine. Over the last 40 years, we have perfected computer methods and experiments to understand and predict the performance of this amazing part of the engine. Our facilities allow us to study the heat transfer in great detail and to simulate real conditions using scale models. There are special equations in what we call ‘dimensionless groups', where certain parameters behave the same at all scales. For example, you could put an Airfix-size Concorde in a Mach 2 wind tunnel and see the same patterns of pressure and shock structures that you would see in the real thing – although you might need to strengthen the model if it’s made from thin plastic!
OSB: What impact might your group's work have on making 'greener' engines?

PI: We have helped to make the engine more fuel-efficient by reducing inefficiencies caused by aerodynamic losses and cooling air. The ultimate aim of most of our research is to reduce CO2 emissions from jet engines.

OSB: Do you expect to see any major changes in jet engines over the next few decades?
PI: Yes. The engine architecture used for passenger Civil Aircraft, such as the Boeing 787 and Airbus 380, has been stable for many years. I think engine configuration will change significantly for future generations of aircraft. We can make engines more efficient by increasing the proportion of air passing through the propellers outside of the core jet intake, called the ‘bypass ratio’. However, these efficiency gains are reduced as we need to build ever-larger casings, called ‘nacelles’, around the propellers that add weight and drag. A new generation of engines called ‘open rotor’ are designed to work without needing nacelles, offering greatly improved efficiencies. I look forward to seeing these technologies develop in years to come.